Series Magnetic Circuits

In other words, Magnetic circuit problems, are basically of two types. In one type, $\Phi$ is given, and the impressed $mmf=NI$ must be computed. This is the type of problem encountered in the design of motors, generators, and transformers. In the other type, NI is given, and the flux $\Phi$ of the magnetic circuit must be found. This type of problem is encountered primarily in the design of magnetic amplifiers and is more difficult since the approach is "hit or miss." As indicated in earlier discussions, the value of $\mu$ will vary from point to point along the magnetization curve. This eliminates the possibility of finding the reluctance of each "branch" or the "total reluctance" of a network, as was done for electric circuits where R had a fixed value for any applied current or voltage. If the total reluctance could be determined, $\Phi$ could then be determined using the ohm's law analogy for magnetic circuits. For magnetic circuits, the level of $B$ or $H$ is determined from the each other using the B-H curve, and $\mu$ is seldom calculated unless asked for. An approach frequently employed in the analysis of magnetic circuits is the table method. Before a problem is analyzed in detail, a table is prepared listing in the extreme left-hand column the various sections of the magnetic circuit. The columns on the right are reserved for the quantities to be found for each section. In this way, the individual doing the problem can keep track of what is required to complete the problem and also of what the next step should be. After a few examples, the usefulness of this method should become clear. In each example, the magnitude of the magnetomotive force is to be determined.